All brain MRIs were performed on a single Siemens Prisma 3T scanner with standard Siemens 64-channel RF receiver head coil. All subjects received anatomical T1-weighted and T2-weighted fluid-attenuated inversion recovery (FLAIR) imaging and dMRI. The imaging sequences and parameters of the anatomical scans followed the Alzheimer's Disease Neuroimaging Initiative 2 protocols (http://adni.loni.usc.edu/methods/documents/mri-protocols/ ) and were reviewed by neuroradiologists for incidental findings.
The dMRI protocol used a single-shot spin-echo echo-planar imaging sequence with a HYDI scheme that contained three zero diffusion-weighting (i.e., b-value = 0 s/mm2) and five concentric diffusion-weighting shells (b-values = 0, 250, 1000, 2000, 3250, 5000 s/mm2) with 142 diffusion-weighting gradient directions [44] (link). The field of view was 240 × 240 mm with an imaging matrix of 120 × 120 and 68 slices of 2-mm slice thickness, yielding 2-mm isotropic voxels. An additional b = 0s/mm2 with reversed-phase encoding was acquired for geometric distortion correction.
The dMRI protocol used a single-shot spin-echo echo-planar imaging sequence with a HYDI scheme that contained three zero diffusion-weighting (i.e., b-value = 0 s/mm2) and five concentric diffusion-weighting shells (b-values = 0, 250, 1000, 2000, 3250, 5000 s/mm2) with 142 diffusion-weighting gradient directions [44] (link). The field of view was 240 × 240 mm with an imaging matrix of 120 × 120 and 68 slices of 2-mm slice thickness, yielding 2-mm isotropic voxels. An additional b = 0s/mm2 with reversed-phase encoding was acquired for geometric distortion correction.